1. Field of the Invention
The present invention relates to a carbon nanotube (“CNT”) gas sensor and a method of manufacturing the same, and more particularly, to a CNT gas sensor that has low operating temperature, low power consumption, and high sensitivity and a method of manufacturing the CNT gas sensor.
2. Description of the Related Art
Generally, a gas sensor measures the amount of a harmful gas using the characteristics of varying electrical conductivity or electrical resistance according to adsorption of gas molecules. Conventionally, a gas sensor was manufactured using a metal oxide semiconductor (“MOS”), a solid electrolyte material, or organic materials. However, the gas sensor that uses the MOS or the solid electrolyte material starts a sensing operation when the gas sensor is heated to 200-600° C. The gas sensor that uses the organic material has a very low electrical conductivity, and the gas sensor that uses carbon black and an organic complex has a very low sensitivity. In particular, when the gas sensor is manufactured using a complex of carbon black and an organic material, the gas sensor shows very low sensitivity.
Carbon nanotubes (“CNTs”) have recently drawn attention as a new material that can be applied to various industrial fields due to their high electron emission characteristics and high chemical reactivity. In particular, the CNT is a material that has a very wide surface area compared to the volume of the CNT. Therefore, the CNT is very useful in fields such as hydrogen storing and the detection of a minor chemical component together with high surface reactivity. The advantages of the CNTs are derived from the properties of the CNTS. The CNTs, which are rolled carbon molecules formed by rolling graphite plates into cylinders (composed of sp2 bonds) that consist of carbons connected by hexagonal rings, and have a diameter of a few to a few tens of nanometers nm. The CNTs are strong, flexible, and do not easily wear despite repeated use, and have different electrical characteristics according to the shape of their rolled up structure and diameter.
When the CNTs are used in a gas sensor, there are advantages in that a sensing operation can start at room temperature, and sensitivity and speed of response are very high since there is a large variation in electrical conductivity when harmful gases such as NH3 or NO2 react with the CNTs in the gas sensor.
There is a conventional gas sensor in which CNTs are grown between field effect transistor (“FET”) type electrodes using a chemical vapor deposition (“CVD”) method. At this time, the CNTs are grown using a solution in which CNT bundles are uniformly distributed in a solvent, for example, dimethylformamide, chloroform, dichloroethane, or methylpyrrolidinone.
However, the kinds of solvent in which the CNTs can be distributed are limited. Also, when the gas sensor is used for a long period of time, stability of the gas sensor is reduced due to low adhesiveness between the electrodes having a very fine structure and the CNTs. Furthermore, the reproducibility of the CNT sensor layer is difficult due to the characteristics of the CVD method. In particular, in the case of a gas sensor in which a few CNT elements having high sensitivity are connected, the manufacturing reproducibility can be very important. Also, since the CNTs are stacked to a very low height in a thin film state (in particular, when the CNTs are horizontally grown), a sensing space is formed to be very small and sensitivity is very low. Therefore, there is a difficulty in detecting a stable gas such as carbon dioxide.